1. Field of the Invention
The present invention relates to an image formation device such as a laser beam printer, an LED array printer and a digital copying machine for forming a multicolor image using arrayed light sources, particularly relates to an image formation device which can be miniaturized, of which the quality of an image is uniform, which can form a high resolution of color image at high speed and in which the deterioration of color registration can be reduced even if the relative position of a light source and an optical element is dislocated.
2. Description of the Related Art
A conventional type image formation device emits a laser beam modulated according to a picture signal from a laser beam source for example, scans the laser beam in a horizontal scanning direction using a polygon mirror, exposes a photoconductor drum rotated in a vertical scanning direction by the laser beam scanned using the polygon mirror, forms an electrostatic latent image on the photoconductor drum by the above exposure scanning and implements the recording of an image based upon the electrostatic latent image.
However, according to the light deflection type image formation device using a polygon mirror, as the speedup of the rotational speed of the polygon mirror is limited, the speedup of recording rate is limited.
To speed up the recording rate of an image formation device, an image formation device using arrayed light sources for emitting plural light beams by driving according to the pattern of a recorded image without a polygon mirror is being studied.
A conventional type image formation device not using a polygon mirror is disclosed in Japanese Published Unexamined Patent Application No. Hei 9-193450 for example.
FIG. 21 shows the image formation device. The image formation device is provided with a laser array 100 having plural laser beam emitting elements 100a arrayed in a horizontal scanning direction, a photoconductor drum 105 exposed by plural laser beams 101 emitted from each laser beam emitting element 100a on which an electrostatic latent image according to a picture signal is formed by moving the photoconductor drum in a vertical scanning direction differently from the laser array 100, a field lens 102 as a projection optical system for focusing plural laser beams 101 emitted from plural laser beam emitting elements 100a on a common focus 106, an imaging lens system 107 arranged on the focus 106 as a projection optical system for imaging the plural laser beams 101 on the photoconductor drum 105 and forming plural beam spots on the photoconductor drum 105, a half mirror 103 arranged between the field lens 102 and the imaging lens system 107, a photo detecting element 104 for detecting the luminous energy of a laser beam reflected by the half mirror 103 and a control part for controlling the driving condition of each laser beam emitting element 100a based upon a signal detected by the photo detecting element 104.
Hereby, as plural laser beam emitting elements 100a can be simultaneously driven according to the pattern of a recorded image, a recording rate can be sped up. As the laser beam emitting elements 100a can be arranged in high density, a high resolution of image can be acquired. Also, as each laser beam emitting element 100a can correct luminous energy, luminous energy can be kept uniform and a uniform image can be acquired.
There is known a multicolor image formation device using a light emitting element array in which multiple light emitting elements are arranged corresponding to the scanning width of an output image as a light source for projecting by an optical system and forming an image on a photoconductor as disclosed in Japanese Published Unexamined Patent Application No. Hei 8-181871 for example.
FIGS. 22A and 22B show the conventional type multicolor image formation device. The multicolor image formation device is provided with plural light emitting diode (LED) arrays 101Y, 101M, 101C and 101K respectively provided corresponding to yellow (Y), magenta (M), cyan (C) and black (K) in which each LED is arranged in the direction of the width of an image (a horizontal scanning direction), driving circuits 10Y, 100M, 100C and 100K for driving each LED array 110Y, 10M, 101C and 101K based upon Y image data, M image data, C image data and K image data respectively corresponding to Y, M, C and K and emitting plural light beams 102y, 102m, 102c and 102k, photoconductor drums 104Y, 104M, 104C and 104K arranged along a traveling route 105 of paper P corresponding to each color and rotated in a direction shown by an arrow (in a vertical scanning direction) and projection optical systems 103Y, 103M, 103C and 103K for respectively projecting and imaging plural light beams 102y, 102m, 102c and 102k respectively from the LED arrays 101Y, 101M, 101C and 101K on the photoconductor drums 104Y, 104M, 104C and 104K as shown in FIG. 22A.
The LED array 101 is attached to a case 106 via a mounting plate 107 as shown in FIG. 22B and the projection optical system 103 is attached to the case 106 via a mounting member 108 so that it is located immediately under the LED array 101. Hereby, as plural LEDs can be simultaneously driven according to the pattern of a recorded image, a color image can be recorded at high speed.
However, according to the conventional type image formation device, if the laser array, the LED array, the projection optical system and a luminous energy detecting system are provided for every color to form a color image, there is a problem that the device is large-sized.
According to the conventional type multicolor image formation device, as the projection optical system is independent for every color, the exposed position of each color is dislocated when the position of the LED array and an optical element changes because of the change of temperature, vibration and the like and so-called color registration is deteriorated. As a result, a problem arises that the quality of an output image is deteriorated.